A switching function that dynamically switches between optical transmission routes is desired in optical transmission systems today. For example, if a fault occurs in a given route, immediately establishing a bypass route is desirable.
Reachability determination is performed on a new optical transmission route candidate when an optical transmission route is switched from one to another. Reachability determination is performed on the optical transmission route by comparing a communication quality obtained when an optical signal is transmitted along the optical transmission route as a measurement target with a threshold value of the communication quality permissible in the system. If the optical transmission route is determined as reachable, route switching is performed so that the optical signal is transmitted through the optical transmission route. If the optical transmission route is determined as not reachable, the reachability determination is performed on a next candidate.
The switching between the optical transmission routes is desirably completed within a short period of time. In particular, the switching between the optical transmission routes subsequent to the occurrence of a fault is to be performed within a short period of time. To switch from one optical transmission route to another within a short period of time, the route reachability determination is desirably performed on the optical transmission route.
If the route reachability determination is performed in advance on all the routes between desired nodes, and the results are stored on a network management server, it is possible to perform the route reachability determination on the optical transmission route within a short period of time. However, the number of routes to perform the transmission reachability determination on is too large in a large-scale network, and costs involved become prohibitive.
To address this problem, a method of determining reachability of the route in an autonomous fashion in an optical communication network has been disclosed (Japanese Laid-open Patent Publication No. 2009-118101). In the disclosed method, each optical network apparatus stores as a database a parameter related to the size of a factor contributing to signal degradation, and the parameter is relayed via a path route through which a signal passes. Each optical network apparatus cumulatively adds a parameter thereof to the value of a received parameter, and then transmits the resulting value to a next optical network apparatus. An optical network apparatus that serves as a terminal of the path estimates the size of the signal degradation of all the paths using the received parameter, and thus determines whether the path is able to transmit the signal at a quality equal to or higher than a specific level.